The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to control of a carrier head for a chemical mechanical polishing system.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer during photolithography. Therefore, there is a need to periodically planarize the substrate surface to provide a substantially planar layer surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted to a carrier or polishing head. The exposed surface of the substrate is then placed against a moving polishing pad. The carrier provides a controllable load on the substrate to press it against the polishing pad. A retaining ring can be used to center the substrate onto the carrier to prevent it from slipping laterally. By applying the downward force, while rotating the slurry-covered pad for a selected amount of time, a desired amount of material can be removed from the upper surface of the substrate to planarize it.
In order to obtain spatially uniform polishing across the surface of a wafer, it may be desirable to vary the pressure applied to the substrate at different locations. For example, it may be desirable to vary the pressure applied to different portions of the substrate to compensate for uneven polishing pad wear, non-uniform slurry distribution, or other sources of spatial non-uniformity in the polishing rate.
Accordingly, there is a need for a chemical-mechanical polishing method and apparatus that enables the user to vary the pressure applied to different regions of the wafer in a controlled manner, when it is desirable to enhance polishing uniformity.
In one aspect, the invention is directed to a polishing system that has a carrier head with a plurality of pressurizable chambers, a common pressure regulation line having a first pressure, a plurality of second lines having a second pressure that is different than the first pressure, and a plurality of first valves. Each first valve is associated with one of the pressure chambers and is actuatable between a first position in which the first valve fluidly couples its associated pressure chamber with the common pressure regulation line and a second position in which the first valve fluidly couples its associated pressure chamber with one of the plurality of second lines.
Implementations of the invention may include one or more of the following features. The polishing system may include a pressure regulator and a second valve. The second valve may be actuatable between a first position in which the second valve fluidly couples the common pressure regulation line to the pressure regulator and a second position in which the common pressure regulation line is not fluidly coupled to the pressure regulator. In the second position the second valve may fluidly couple the common pressure regulation line to a vacuum source. The plurality of second lines may each vent to atmospheric pressure or may be coupled to a second common pressure regulation line. The polishing system may include a first pressure regulator, a second pressure regulator, a second valve, and a third valve. The second valve may be actuatable between a first position in which the second valve fluidly couples the common pressure regulation line to the first pressure regulator and a second position in which the common pressure regulation line is not fluidly coupled to the first pressure regulator, and the third valve may be actuatable between a first position in which the third valve fluidly couples the second common pressure regulation line to the second pressure regulator and a second position in which the second common pressure regulation line is not fluidly coupled to the second pressure regulator. In the second position the second valve may fluidly couple the common pressure regulation line to a vacuum source. In the second position the third valve may fluidly couple the second common pressure regulation line to a vent.
In another aspect, the invention is directed to a method for chemical mechanical polishing of a substrate. In the method, a substrate is pressed against a polishing pad with a carrier head having a plurality of chambers, relative movement is caused between the polishing pad and the substrate, and a common first pressure is applied to a plurality of chambers in the carrier head using a common regulator. A duration of application of the first pressure to each chamber from the plurality of chambers is controlled independently from other chambers.
Implementations of the invention may include one or more of the following features. A second pressure may be applied to a second chamber that controls a pressure on the substrate, and the second pressure may be controllable independently of the first pressure. A third pressure may be applied to a third chamber, and the third pressure may be controllable independently of the first and second pressures. The second pressure may be applied against an edge portion of the backside of the substrate, whereas the third pressure may be applied to a retaining ring surrounding the perimeter of the substrate to press the retaining ring against the polishing pad to retain the substrate. The substrate may be substantially circular, and the first pressure may be applied by the plurality of chambers to a portion of the substrate surrounded by the edge portion. The portion of the substrate surrounded by the edge portion may include a plurality of concentric zones, and each chamber from the plurality of chambers may apply the first pressure to one of the concentric zones from the plurality of concentric zones.
In another aspect, the invention is directed to a method for controlling the polishing pressure over the regions of a substrate in a chemical mechanical apparatus. In the method, a first pressure exerted on an edge region of the substrate is controlled by a first pressure regulator, and a second pressure exerted on a plurality of the substrate regions, other than the edge region, is controlled by a second pressure regulator. The amount of material removed from each region of the plurality of regions is controlled independently from other regions.
In another aspect, the invention is directed to a polishing system with a carrier head and a pressure controller. The carrier head includes a flexible membrane providing a substrate-mounting surface and a retaining ring joined to the base assembly. The volume between the base assembly and the flexible membrane forms a first chamber and a plurality of second chambers. The pressure controller applies a first pressure to the retaining ring, a second pressure to the first chamber and a first portion of the substrate, and a third pressure to the plurality of second chambers. Each of the plurality of second chambers applies the third pressure to an associated segment of the substrate.
Implementations of the invention may include one or more of the following features. A controller may independently control a duration of application of the third pressure to each chamber from the plurality of second chambers.